I need to resize a bunch of PVCs. It seems the easiest way to do it is through the ExpandPersistentVolumes feature. I am however having trouble getting the configuration to cooperate.

The ExpandPersistentVolumes feature gate is set in kubelet on all three masters, as shown:

(output trimmed to relevant bits for sanity)

$ parallel-ssh -h /tmp/masters -P "ps aux | grep feature"
172.20.53.249: root     15206  7.4  0.5 619888 83952 ?        Ssl  19:52   0:02 /opt/kubernetes/bin/kubelet  --feature-gates=ExpandPersistentVolumes=true,ExperimentalCriticalPodAnnotation=true
[1] 12:53:08 [SUCCESS] 172.20...
172.20.58.111: root     17798  4.5  0.5 636280 87328 ?        Ssl  19:51   0:04 /opt/kubernetes/bin/kubelet --feature-gates=ExpandPersistentVolumes=true,ExperimentalCriticalPodAnnotation=true
[2] 12:53:08 [SUCCESS] 172.20...
172.20.53.240: root      9287  4.0  0.5 645276 90528 ?        Ssl  19:50   0:06 /opt/kubernetes/bin/kubelet --feature-gates=ExpandPersistentVolumes=true,ExperimentalCriticalPodAnnotation=true
[3] 12:53:08 [SUCCESS] 172.20..

The apiserver has the PersistentVolumeClaimResize admission controller, as shown:

$ kubectl --namespace=kube-system get pod -o yaml | grep -i admission                                                                                                                                                           
    /usr/local/bin/kube-apiserver --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota
    /usr/local/bin/kube-apiserver --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota
    /usr/local/bin/kube-apiserver --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota

However, when I create or edit a storage class to add allowVolumeExpansion, it is removed on save. For example:

$ cat new-sc.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  creationTimestamp: null
  labels:
    k8s-addon: storage-aws.addons.k8s.io
  name: gp2-2
  selfLink: /apis/storage.k8s.io/v1/storageclasses/gp2
parameters:
  encrypted: "true"
  kmsKeyId: arn:aws:kms:us-west-2:<omitted>
  type: gp2
  zone: us-west-2a
provisioner: kubernetes.io/aws-ebs
reclaimPolicy: Delete
allowVolumeExpansion: true

$ kubectl create -f new-sc.yaml
storageclass "gp2-2" created

$ kubectl get sc gp2-2 -o yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  creationTimestamp: 2018-05-22T20:00:17Z
  labels:
    k8s-addon: storage-aws.addons.k8s.io
  name: gp2-2
  resourceVersion: "2546166"
  selfLink: /apis/storage.k8s.io/v1/storageclasses/gp2-2
  uid: <omitted>
parameters:
  encrypted: "true"
  kmsKeyId: arn:aws:kms:us-west-2:<omitted>
  type: gp2
  zone: us-west-2a
provisioner: kubernetes.io/aws-ebs
reclaimPolicy: Delete

What am I missing? What is erasing this key from my storageclass configuration?

EDIT: Here is the command used by the kube-apiserver pods. It does not say anything about feature gates. The cluster was launched using Kops.

- /bin/sh
    - -c
    - mkfifo /tmp/pipe; (tee -a /var/log/kube-apiserver.log < /tmp/pipe & ) ; exec
      /usr/local/bin/kube-apiserver --address=127.0.0.1 --admission-control=Initializers,NamespaceLifecycle,LimitRanger,ServiceAccount,PersistentVolumeLabel,DefaultStorageClass,DefaultTolerationSeconds,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,NodeRestriction,PersistentVolumeClaimResize,ResourceQuota
      --allow-privileged=true --anonymous-auth=false --apiserver-count=3 --authorization-mode=RBAC
      --basic-auth-file=/srv/kubernetes/basic_auth.csv --client-ca-file=/srv/kubernetes/ca.crt
      --cloud-provider=aws --etcd-cafile=/srv/kubernetes/ca.crt --etcd-certfile=/srv/kubernetes/etcd-client.pem
      --etcd-keyfile=/srv/kubernetes/etcd-client-key.pem --etcd-servers-overrides=/events#https://127.0.0.1:4002
      --etcd-servers=https://127.0.0.1:4001 --insecure-port=8080 --kubelet-preferred-address-types=InternalIP,Hostname,ExternalIP
      --proxy-client-cert-file=/srv/kubernetes/apiserver-aggregator.cert --proxy-client-key-file=/srv/kubernetes/apiserver-aggregator.key
      --requestheader-allowed-names=aggregator --requestheader-client-ca-file=/srv/kubernetes/apiserver-aggregator-ca.cert
      --requestheader-extra-headers-prefix=X-Remote-Extra- --requestheader-group-headers=X-Remote-Group
      --requestheader-username-headers=X-Remote-User --secure-port=443 --service-cluster-ip-range=100.64.0.0/13
      --storage-backend=etcd3 --tls-cert-file=/srv/kubernetes/server.cert --tls-private-key-file=/srv/kubernetes/server.key
      --token-auth-file=/srv/kubernetes/known_tokens.csv --v=1 > /tmp/pipe 2>&1